Rugby authorities have been accused of repeating the mistakes made by the US NFL in dismissing evidence that repeated concussions could be a contributory factor in the early on-set of dementia.

In the summer in excess of 4,500 former NFL players agreed a £476m settlement for concussion-related brain injuries sustained during their American football careers. Some of the players were suffering from dementia, depression or Alzheimer's as a result of the bangs on the head they received during their time in the game.

Despite that, this week the IRB and RFU claimed "no causal link" has been proved between concussions and CTE, although the RFU has agreed to introduce compulsory training of all those involved in the game to make them aware of the risks of concussion.

The RFU's head of medicine Dr Simon Kemp has previously said there is no proven association between head trauma and dementia, but Dr Michael Grey, a reader in motor neuroscience at the University of Birmingham's School of Sport, Exercise and Rehabilitation Sciences, disagreed. "Rubbish. We have very good evidence of the link between concussion and dementia.

"'Scientifically proven' - that was the phrase used to deny the link between cigarettes and cancer. It's an easy thing to say. Have we scientifically proved it? There is very good evidence now that multiple concussions can lead to premature ageing and neurodegenerative diseases such as Parkinson's. That danger is very real."

"Across the world's top experts in neuroscience there is absolutely no discussion, no debate, about whether dementia associated with traumatic brain injury exists," Dr Willie Stewart, a neuropathologist at Glasgow Southern General Hospital, told the Mail on Sunday. "The debate is around the minutiae of the disease, not whether or not it exists.

"Among people who work in this field, we are all in consensus that post-traumatic degeneration of the brain exists. There are many questions which remain unanswered, such as the number of concussions required to cause CTE. But there is no question over a link between the two."

Earlier in the week former IRB medical adviser Barry O'Driscoll, who resigned last year in frustration at its continuing stance on concussion, said: "I believe the lawyers are licking their lips."